Maurice Delanne (Duo-Mono)

I got several mails telling that I still miss a page about the
Delanne airplanes in my tandemwing section. They were right.

After I received more info about the Delanne concept (Magazine:
Air trails, october 1950 and Le fana de l' aviation, Dec. 1988)
(thank you, Paul Deweer and Brian Ward), I noticed that this
concept is nearly forgotten, while it has the potential to solve
some current problems in light and passengers aviation. Later more
about that. Let me first explain how the concept works, its
advantages and disadvantages and how it was tested.

Maurice Delanne had his own idea about airplanes. He thought that
the airplanes were too heavy and they needed a huge engine (adding
more weight) to get them in the air. His first own design (a three
seater low wing monoplane) which was to be build in his own factory
was as good the structural patents were acquired by the French Air
Ministry! Due to the lighter weight the performance was better.

Now it was time for Maurice Delanne to learn to fly himself. He
notes that he was not such a bright pupil. The airplanes at that
time needed to be flown at a regular rate to be able to steer them
correctly. You needed experience! That was the reason why so little
people flew. Not everybody had the time or money to fly each day.
Delanne's idea was to simplify flying so it would attract more
people. Attracting more people would lead to more airplanes and ...
to a large airplane industry. So, he needed to built a airplane for
the Sunday-flier. Delanne wanted:

stability

quick take off and landing (only needing short
airstrips)

no stall

no complex devices (to increase lift) and the resulting
low cost

high cruise speed

He knew about the shortcomings of the conventional airplane and
heard about the promising possibilities of tandemwings. Even though
it has a lower performance due to the interference between both
wings, Delanne was convinced that the solution for his problem was
to be found in that configuration. He started his tests in
1932.

Quickly he noticed the advantages of this concept in a wind
tunnel. Go see the part I wrote about the slotted wing in the page
of Nenadovitch to better understand it.

But here Delanne did not use a horizontal tail like Nenadovitch
did. He used the rear wing as elevator and ailerons. Also he place
endplates on the rear wing. Doing that he created another
advantage: the air over the rear wing (captured between the two
endplates) was in a delayed stall effect due to the slotted wing
effect. As long as the stall was delayed, the good air flow
over the elevators and ailerons made control at low speeds
possible.

OK, you say, hey, Henri Mignet has a similar advantage. Yep, but
here there is even another advantage: The CG (Center of Gravity)
range is enourmous. Tests showed that it could be placed to 67% of
the mean aerodynamical chord. With other words ... no
tricky centering. Mignets designs are still touchy to that
part. The CG should be at 25% of the total chord. Further backwards
... DEATHLY.

Delanne got funds from the Air Ministry to built a prototype.
The goal was a flying command post. French tactical experts wanted
to have a commander in the air above his fighting squadron. They
needed a two-seater fighter where the rear of the fighter was
protected by a set of guns. That way the pilot-commander could turn
all his attention on his task. Another thing that the French high
placed wanted were braced gull wings. Delanne asked to use a
straight wing. But he could not change their minds.

In the book "The design of the aeroplane" by Darrol Stinton I
found out that they designed eight versions, but only two were
built and flown. The front wing was slightly larger than the rear
wing. In top view the wings leading edges were separated by a
distance of about two times the front wing chord. The vertical
distance was about once the chord of the front wing.

A dihidral of 3° and aspect ratio of 6,78 are
typical for both wings (Quote article in "le Fana de l' Aviation",
Dec. 1988).

Darrol Stinton mentions also that the Arsenal Delanne 10C-2
tandem-wing two-seater fighter with retracting gear had a maximum
level speed ratio (Vc/Vso) of about 7,5. Conventional airplanes
with piston engines and tails normally had 3 to 3,5. So ...
there was a big advantage in speed range. Another
advantage was that a rear turret could be placed too. The British
would experiment with last last advantage with their Westland
Lysander.

To several people the Arsenal Delanne was a proof that a
tandemwing could be beautiful too.